title: Mass spectrometric measurement of end-tidal xenon concentration for clinical stable xenon/computerized tomography cerebral blood flow studies.
abstract: We have demonstrated the feasibility of using a compact dedicated mass spectrometer to monitor end-tidal xenon concentration in human subjects during stable xenon computerized tomography measurements of regional cerebral blood flow. End-tidal carbon dioxide concentration is monitored simultaneously and noninvasively without degrading the dynamic response to xenon. For clinical regional cerebral blood flow studies we employed a Nuclide 3-60-G Sectorr mass spectrometer with a 3 in radius, 60 degrees magnetic sector and a variable (0-5000 V) ion accelerating potential. The required high vacuum (10(-7) Torr) was achieved and maintained by means of a turbomolecular pump. A needlemetering valve was incorporated into an anesthesia mask connector, and exhaled gases were transported to the mass spectrometer via a 6 ft length of Teflon tubing (1/16 in i.d.). Molecular flow conditions between the sample and analysis chambers were provided by use of a gold foil leak (0.0005 in. hole). At an inlet pressure of 400 m Torr (achieved by means of the needle valve), the inlet system was characterized by a gas transport lag-time of 1.3 s and a rise-time constant of 85 ms. Xenon (doubly charged ion: m/z 68) and carbon dioxide (doubly charged ion: m/z 22) were monitored alternately at 75 ms intervals. Our experience with mass spectrometry has demonstrated the feasibility of using a compact dedicated instrument for accurately and non-invasively monitoring end-tidal xenon concentration in a clinical setting.
mesh_terms: D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging*; D002245:Carbon Dioxide / Q000032:analysis; D002560:Cerebrovascular Circulation; D006801:Humans; D013058:Mass Spectrometry / Q000295:instrumentation; D008991:Monitoring, Physiologic; D012039:Regional Blood Flow; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000295:instrumentation; D014978:Xenon / Q000032:analysis*
chemical_list: D002245:Carbon Dioxide; D014978:Xenon